1. Field
The present invention generally relates to the shape of an aircraft fuselage and, in particular, to a fuselage feature that reduces drag for transonic aircraft.
2. Description of the Related Art
The speed of aircraft that are traveling near or above the speed of sound is often given as a “Mach number,” i.e. a dimensionless number that is the speed of the aircraft divided by the speed of sound. Vehicles moving at speeds well below Mach 1 are referred to as “subsonic” while vehicles moving at speeds well above Mach 1 are referred to as “supersonic.” Vehicles traveling at speeds in the range of Mach 0.7-1.1 are referred to as “transonic” as the air flowing past the aircraft may locally be either above or below Mach 1.
Shockwaves can be generated by aircraft at locations where the local air velocity is at or above Mach 1. Transonic flow dynamics are nonlinear and drag on the aircraft increases significantly in regions where the air velocity locally exceeds Mach 1 and then “shocks” back to subsonic speed. The range of a subsonic aircraft increases as the speed increases. Thus, it is desirable for a subsonic aircraft to fly as close to Mach 1 as possible. When the speed of an aircraft enters the transonic region, however, the increased drag caused by shockwaves formed in regions where the air velocity exceeds Mach 1 may negate any additional gains in efficiency by further increases in speed or even reduce the overall efficiency if the speed is increased further.